High density photonic lightwave circuits have been the subject of significant investigation recently. High index contrast waveguide-based devices (e.g., modulators or attenuators) and devices such as photodetectors and modulators formed from silicon-compatible materials (e.g., germanium or SiGe) are fabricated using complementary metal-oxide-semiconductor (CMOS) processing technology onto silicon or silicon-on-insulator (SOI) substrates. For instance, photodetectors formed of one or more layers of Ge or SiGe on a Si substrate that detects light incident from the top or bottom of the substrate have been studied. Such photodetectors, when monolithically integrated with CMOS integrated circuits on the same substrate, are often fabricated from thin films of Ge and SiGe that are inefficient at absorbing incident light from the top or bottom of the substrate.